1. Field of the Invention
In general, the present invention relates to a barrel finishing machine. More particularly, the present invention relates to such a machine that includes means for producing a rotating magnetic field and for varying the rotating magnetic field in such a way that multiple different flows or motions are produced in a mixture of workpieces and an abrasive medium, thereby freeing the workpieces from the abrasive medium and subjecting the workpieces to a finishing action by the abrasive medium.
2. Description of the Prior Art
A metal finishing machine is described in two Japanese patent applications. One is published for opposition under the examined publication No. 4-26981 and the other is laid open to public inspection under the unexamined publication No. 60-118466. In both of the applications, the machine is designed to produce a magnetic field and vary the magnetic field by rotation in such a manner that flows or motions of workpieces and an abrasive medium are produced in multiple different ways within a container, thereby freeing the workpieces from the abrasive medium and subjecting the workpieces to a finishing action by the abrasive medium.
The conventional machine has the following disadvantages and problems. If the container that contains the workpieces and the abrasive medium is placed in the center on a rotary disk on which permanent magnets are mounted, the workpieces will tend to be finished unevenly. Thus, extra time must be required until the finishing process is completed. The magnets that produce the magnetic fields are arranged regularly. That is every adjacent magnet has its respective polarity alternating like NS, NS, and so on. This regular arrangement of polarities may produce flows or motions of the works and abrasive media that occur repeatedly but regularly. Sometimes, this presents a defect that causes the irregular finishing action against the works or a requirement of extra time for the finishing operation for completion.
For example, the regular arrangement of polarities such as N, S, N, S, and so on, as described above, produces circumferential or concentric flows or motions of the abrasive medium as shown by arrows 21 in FIG. 7, which are formed into loops 22 in FIG. 8.
It may readily be understood that a container 23 that contains workpieces and abrasive medium (which includes ferromagnetic substances, abrasive media, compounds, and the like) must be placed within the region 24 influenced by the magnetic action (FIG. 9). As the region 24 is formed like a doughnut, it is clear that the container 23 must have a diameter that is equal to half the diameter of the rotary disk 25 or smaller.
Assuming, for example, that the container 23 has the same diameter as the rotary disk 25, no loop such as the loop 22 would be produced in the center 26 where the finishing action would occur inadequately. As a whole, the workpieces would have an uneven finishing action.